Ballistic resistant sheets comprising multiple monolayers containing unidirectionally (UD) oriented reinforcing fibers with a matrix material are known, e.g., from U.S. Pat. Nos. 4,623,574, 5,766,725 and 7,527,854 and U.S. Patent Application Publication No. 2010/0064404 (the entire contents of each being expressly incorporated hereinto by reference).
A ballistic resistant sheet is furthermore known from WO2012/150169. In this publication a two-layer hybrid structure is disclosed comprised of a first layer (‘first stack’) comprising laminates with a first kind of yarn, and of a second layer (‘second stack’) comprising laminates with a second kind of yarn. The first kind of yarn and the second kin of yarn differ in linear density or thickness. Some matrix materials are mentioned at page 3, including elastomer and epoxy resin. The examples disclose different types of aramid fibers and styrene-isoprene-styrene block copolymer as matrix material. There is no mention of a 3 layer fiber based hybrid structure.
A ballistic resistant sheet is known from WO2008/077605. This publication discloses the manufacture of ballistic resistant sheets, whereby the ballistic resistant sheet is built up from monolayers with unidirectional polyethylene fibers and a matrix material. The matrix material disclosed in the example is a styrene-isoprene-styrene block copolymer. Furthermore a ballistic resistant molded article is disclosed based on compressed ballistic resistant sheets combined with a ceramic strike face, optionally with a metal layer between the ceramic strike face and the ballistic resistant sheet. Again there is no mention of a 3 layer fiber based hybrid structure.
A ballistic resistant sheet and a composite article is furthermore known from US2012/0156452. In this publication composite structures are disclosed having a plurality of fibers which are at least partially embedded with a matrix. The fibers may be adhered to the matrix at a (varying) level of adhesion. The adhesion level between the fibers and the matrix may be varied spatially within the composite article, e.g. along the length of one of the fibers, or among the fibers in a given layer, or the adhesion may vary between layers of the composite article with the intention to increase the energy absorption of the composite article, i.e. improving bullet stopping ability of the composite article.
A ballistic resistant sheet is also known from WO2005/066577. In this publication sheets are disclosed comprising monolayers of unidirectionally oriented fibers with a strength of at least 1.2 GPa and a modulus of at least 40 GPa and a binder, and a porous separating film at the outer surfaces of the ballistic resistant sheet.
There is continuous drive towards improved ballistic resistant articles, including soft ballistic articles and moulded articles. Such improvements may include articles with improved drapeability. Improved drapeability means an improved wearing comfort of a vest, while at the same time the ballistic protection is not significantly reduced. Alternatively it can relate to about constant wearing comfort while the ballistic protection is improved. Preferably the ballistic protection is further improved. Such ballistic protection may relate to the bullet stopping characteristics, often referred to as V50—where 50% of the bullets are stopped—which may also be expressed as ballistic energy absorption, or V0 where all bullets are stopped by the ballistic resistant article, or reduction of trauma or backface deformation. The ballistic resistant sheets offer protection against e.g. bullets and ballistic fragments.
It is towards providing such ballistic resistant sheets and soft ballistic articles therefrom that the present invention is specifically directed.
In general, the embodiments disclosed herein relate to hybrid ballistic resistant sheets, articles which comprise such sheets and methods of making the same. According to some embodiments, the ballistic resistant sheets will include a core layer and face layers. The core layer may include at least one, preferably at least two, first monolayer comprised of first unidirectionally (UD) oriented fibers and a matrix material, while the face layers and may include at least one, preferably at least two, second, respectively third, monolayers comprised of second, respectively third UD oriented fibers, herein also referred to as UD fibers, and a matrix material.
Generally, the ballistic resistant sheet of the invention includes at least one core layer and outer layers, herein referred to as face layers, numbered therewith forming a 3 layer hybrid structure of ‘face layer/core layer/face layer’. One of these outer layers, or face layers, will typically face the threat or impact, in the art referred to as strike face, while the other outer layer will be most remote from the threat. Such layer is in the art often referred to as back face. The core layer and face layers may be built up from monolayers or from pre-assembled sets of monolayers, herein referred to as sub-sheets. Each of the outer layers or face layers may be identical or have a different structure and/or composition.